U.S. patent number 5,709,921 [Application Number 08/555,471] was granted by the patent office on 1998-01-20 for controlled hysteresis nonwoven laminates.
This patent grant is currently assigned to Kimberly-Clark Worldwide, Inc.. Invention is credited to Susan Elaine Shawver.
United States Patent |
5,709,921 |
Shawver |
January 20, 1998 |
**Please see images for:
( Certificate of Correction ) ** |
Controlled hysteresis nonwoven laminates
Abstract
There is provided herein a multilayer material comprised of
layers of elastomeric films, fiber, or webs wherein at least one
layer is comprised of an elastomeric polyolefin and at least one
additional layer is comprised of an elastomer selected from the
group consisting of polyurethanes, copolyether esters, polyamide
polyether block copolymers, ethylene vinyl acetates (EVA), and
block copolymers having the general formula A-B-A', A-B-A-B or A-B
like copoly(styrene/ethylene-butylene),
(polystyrene/poly(ethylene-butylene)/polystyrene), and
poly(styrene/ethylene-butylene/styrene). Such a material also
includes at least one gatherable web to which the elastic webs are
joined and may be made into a personal care product, an infection
control product, a protective cover or a garment.
Inventors: |
Shawver; Susan Elaine (Roswell,
GA) |
Assignee: |
Kimberly-Clark Worldwide, Inc.
(Irving, TX)
|
Family
ID: |
24217383 |
Appl.
No.: |
08/555,471 |
Filed: |
November 13, 1995 |
Current U.S.
Class: |
428/152; 442/328;
442/396; 442/340; 428/903; 442/388 |
Current CPC
Class: |
B32B
37/206 (20130101); B32B 27/00 (20130101); B32B
37/144 (20130101); B32B 38/06 (20130101); D04H
1/544 (20130101); D04H 1/4291 (20130101); D04H
1/559 (20130101); D04H 1/54 (20130101); D04H
1/56 (20130101); B32B 38/1875 (20130101); B32B
5/00 (20130101); B32B 27/08 (20130101); Y10T
442/601 (20150401); B32B 27/12 (20130101); B32B
2262/0223 (20130101); B32B 7/08 (20130101); B32B
2274/00 (20130101); B32B 2571/00 (20130101); Y10T
428/24446 (20150115); B32B 27/40 (20130101); B32B
2262/023 (20130101); B32B 2437/00 (20130101); B32B
2270/00 (20130101); B32B 2307/726 (20130101); B32B
2556/00 (20130101); B32B 2262/0292 (20130101); B32B
27/34 (20130101); Y10T 442/667 (20150401); B32B
27/32 (20130101); Y10T 442/614 (20150401); B32B
7/12 (20130101); B32B 2262/0261 (20130101); B32B
2535/00 (20130101); Y10S 428/903 (20130101); B32B
27/327 (20130101); B32B 2555/02 (20130101); B32B
2262/0253 (20130101); B32B 2307/51 (20130101); B32B
7/02 (20130101); B32B 2262/0276 (20130101); B32B
5/06 (20130101); B32B 5/26 (20130101); B32B
27/306 (20130101); B32B 27/36 (20130101); B32B
2307/514 (20130101); B32B 2307/54 (20130101); Y10T
442/676 (20150401) |
Current International
Class: |
D04H
13/00 (20060101); B32B 005/04 (); B32B 005/06 ();
B32B 005/26 (); B32B 025/08 (); B32B 025/10 () |
Field of
Search: |
;428/152,286,287,300,301,303,903 |
References Cited
[Referenced By]
U.S. Patent Documents
Foreign Patent Documents
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0 712 892 |
|
May 1996 |
|
EP |
|
4-327211 |
|
Nov 1992 |
|
JP |
|
95/03443 |
|
Feb 1995 |
|
WO |
|
95/05418 |
|
Feb 1995 |
|
WO |
|
Other References
Insite Catalyst Structure/Activity Relationships For Olefin
Polymerization, by J. C. Stevens. Central Research Catalysis Lab,
The Dow Chemical Company. Presented at METCON 1993. Sponsored by
Catalyst Consultants, Inc. .
USA:Touch New Plastic Introduced by Exxon Chemical. Reuter Business
Alert. Sep. 13, 1995. .
USA: Exxon Chemical-First Commercial Scale Production Run of
Metallocene-Based PP Successfully Completed. Reuter Business Alert.
Oct. 4, 1995. .
Oscillating Catalysts: A New Twist For Plastics, By K. B. Wagener.
Science, vol. 267, Jan. 13, 1995. p. 191. .
Oscillating Stereocontrol: A Strategy For The Synthesis Of
Thermoplastic Elastomeric Polypropylene, By Geoffrey W. Coates
& Robert M. Waymouth. Science, vol. 267, Jan. 13, 1995. pp.
217-219. .
Variation Of Poly(Propylene) Microtacticity By Catalyst Selection,
by Scott Collins, et al., Dept. Of Chemistry, Univ. of Waterloo,
Waterloo, Ontario, Canada. Received Dec. 19, 1990. Organometallics
1991, 10, 2061-2068. .
Crystalline-Amorphous Block Polypropylene And Nonsymmetric
Ansa-Metallocene Catalyzed Polymerization, by Geraldo Hidalgo
Llinas, et al., Dept. Of Polymer Science and Engin. Macromolecules
1992, 25, 1242-1253. .
Polyethylene And Ethylene Based Copolymers Made By Dow's Insite
Technology, Presentation by Steven P. Chum, Ph.D., Res. Scientist,
Dow Chemical Company, Freeport, Texas, Jan. 1995. .
Selected Application For Constrained Geometry Catalyst Technology
(CGCT) Polymers, by G.D. Schwank, Polyolefins TS&D, Dow Chem.,
Presented at SPO '92, Sep. 23, 1992. .
Usins Molecular Architecture Control To Design Polymer Performance,
by Gerald Lancaster et al., Presentation at METCON '95, Session
IV--Advances in Metallocene Resins Technology, Houston, Texas, May
1995. .
Dow Constrained Goemetry Catalyst Technology (CGCT): New Rules For
Ethylene a-Olefins Interpolymers-Controlled Rheology Polyolefins,
by S. Lai and G.W. Knight, Antec 1993, pp. 1188-1192. .
Process Technology For Unique Polymer Design Using Dow Constrained
Goemetry Catalyst, by Kurt W. Swogger, et al., Polyolefins &
Elastomers R&D, The Dow Chemical Company, Freeport, Texas.
.
The New Family Of Polyolefins From Insite Technology, by B.A. Story
and G.W. Knight. Polyolefins & Elastomers R&D, The Dow
Chemical Company, Freeport, Texas. .
Polymer Blends And Composites, by John A. Manson and Leslie H.
Sperling, Sec. 9.2, Bicomponent and Biconstituent Fibers, pp.
273-277, Plenum Press, New York..
|
Primary Examiner: Cannon; James C.
Attorney, Agent or Firm: Robinson; James B.
Claims
What is claimed is:
1. A controlled hysteresis composite elastic material comprising a
first layer which is an elastomeric polyolefin layer and which is
joined to at least one other layer comprised of an elastomeric
polymer selected from the group consisting of polyurethanes,
copolyether esters, polyamide polyether block copolymers, ethylene
vinyl acetates (EVA), and block copolymers having the general
formula A-B-A', A-B-A-B or A-B, and which is also joined to a third
layer which is a gatherable web.
2. The material of claim 1 wherein said polyolefin has a
polydispersity of less than 4.
3. The material of claim 1 wherein said third layer is
neckstretched while joined.
4. The material of claim 1 wherein said elastomeric layers are
stretched while joined to said gatherable web.
5. The material of claim 1 wherein said layers are joined together
by a method selected from the group consisting of needlepunching,
adhesive attachment, thermal bonding and extrusion coating.
6. The material of claim 1 wherein said elastomeric layers are
films.
7. The material of claim 1 wherein said at least one other
elastomeric layer is a web comprised of fibers comprised of
polymers selected from the group consisting of polyurethanes,
copolyether esters, polyamide polyether block copolymers, ethylene
vinyl acetates (EVA), copoly(styrene/ethylene-butylene),
(polystyrene/poly(ethylene-butylene)/polystyrene), and
poly(styrene/ethylene-butylene/styrene).
8. The material of claim 1 wherein said first layer is a meltblown
web of microfibers comprising an elastomeric polyolefin having a
polydispersity of less than 4 and said at least one other layer is
a meltblown web comprising
poly(styrene/ethylene-butylene/styrene).
9. A personal care product selected from the group consisting of
diapers, training pants, absorbent underpants, adult incontinence
products, and feminine hygiene products comprised of the meltblown
web material of claim 8.
10. The personal care product of claim 9 which is a diaper.
11. The personal care product of claim 9 which is an absorbent
underpant.
12. The personal care product of claim 9 which is an adult
incontinence product.
13. The personal care product of claim 9 which is a feminine
hygiene product.
14. A controlled hysteresis composite elastic material comprising a
first layer which is a metallocene polyolefin layer comprised of
fibers having an average diameter less than about 10 microns and
which is joined to a second layer comprised of fibers having an
average diameter less than about 10 microns comprised of an
elastomeric polymer selected from the group consisting of
polyurethanes, copolyether esters, polyamide polyether block
copolymers, ethylene vinyl acetates (EVA), and block copolymers
having the general formula A-B-A', A-B-A-B or A-B, which are also
joined to a third layer which is a gatherable web of fibers having
an average diameter greater than about 7 microns.
15. The material of claim 14 in which said first and second layers
are stretched while joined to said third layer.
16. The material of claim 14 which further comprises a another
gatherable web of fibers having an average diameter of greater than
about 7 microns which is joined to said first layer.
17. The material of claim 14 which further comprises a fourth layer
comprised of fibers having an average diameter less than about 10
microns comprised of an elastomeric polymer selected from the group
consisting of polyurethanes, copolyether esters, polyamide
polyether block copolymers, ethylene vinyl acetates (EVA), and
block copolymers having the general formula A-B-A', A-B-A-B or A-B,
joined to said first layer and a fifth layer which is a gatherable
web of fibers having an average diameter greater than about 7
microns joined to said fourth layer, wherein said first second and
fourth layers are stretched while joined.
Description
BACKGROUND OF THE INVENTION
Thermoplastic resins have been extruded to form fibers, films and
webs for a number of years. The most common thermoplastics for this
application are polyolefins, particularly polypropylene, though
each material has its characteristic advantages and disadvantages
visa vis the properties desired in the final products.
Nonwoven fabrics are one type of product which can be made from
such polymers and are useful for a wide variety of applications
such as personal care products like diapers, feminine hygiene
products and incontinence products, infection control products,
garments and many others. The nonwoven fabrics used in these
applications are often in the form of laminates having various
numbers of layers of meltblown fabric and spunbond fabric like
spunbond/meltblown/spunbond (SMS) laminates, SMMS laminates and
even laminates having 6 or more layers.
One particular type of desirable thermoplastic polymer used to make
fibers, films and webs is elastic. One example of a composition for
producing such products is disclosed in U.S. Pat. No. 4,663,220 to
Wisneski et al. wherein the fiber is produced from a polymer which
is an A-B-A' block copolymer where "A" and "A'" are each a
thermoplastic endblock which comprises a styrenic moiety and where
"B" is an elastomeric poly(ethylene-butylene) midblock, and a
polyolefin processing aid.
While polyolefins like polyethylene and polypropylene have
heretofore been non-elastomeric, recent advances in polymer and
catalyst technology have produced a new class of materials known as
metallocene polymers. The polymers produced through the metallocene
process have properties which are different than those produced
through traditional Ziegler-Natta and other systems and some of
these polymers may be elastomeric. Metallocene based elastomeric
polyolefins have stretch and recovery characteristics different
from those elastomers already known.
The inventor has found that a multilayer laminate in which some of
the layers are made from elastomeric polyolefins which may be
produced through the metallocene process, and some of the layers
are produced from traditional elastomers allows one to tailor the
stretch and recovery characteristics of the finished product to a
very high degree. This is believed to be a superior method to that
of merely blending different elastomers prior to fiber production
for a number of reasons; firstly, blends, like chemical reactions,
can be unpredictable and can actually result in a decrease in the
desired properties of the fabric, and secondly, some polymers may
not be miscible or may not be capable of being made into a
blend.
It is an object of this invention to provide laminates having at
least one layer of elastomeric polyolefin with at least one layer
of other elastomeric polymers to allow for greater control of the
properties of materials produced from such laminates.
SUMMARY OF THE INVENTION
There is provided herein a multilayer laminate comprised of layers
of elastomeric films, fiber, or webs wherein at least one layer is
comprised of an elastomeric polyolefin and at least one additional
layer is comprised of an elastomer selected from the group
consisting of polyurethanes, copolyether esters, polyamide
polyether block copolymers, ethylene vinyl acetates (EVA), and
block copolymers having the general formula A-B-A' or A-B like
copoly(styrene/ethylene-butylene),
(polystyrene/poly(ethylene-butylene)/polystyrene), and
poly(styrene/ethylene-butylene/styrene). Such a laminate may be
made into a personal care product, an infection control product, a
protective cover or a garment.
DEFINITIONS
As used herein the term "nonwoven fabric or web" means a web having
a structure of individual fibers or threads which are interlaid,
but not in an identifiable manner as in a knitted fabric. Nonwoven
fabrics or webs have been formed from many processes such as for
example, meltblowing processes, spunbonding processes, and bonded
carded web processes. The basis weight of nonwoven fabrics is
usually expressed in ounces of material per square yard (osy) or
grams per square meter (gsm) and the fiber diameters useful are
usually expressed in microns. (Note that to convert from osy to
gsm, multiply osy by 33.91). As used herein the term "microfibers"
means small diameter fibers having an average diameter not greater
than about 75 microns, for example, having an average diameter of
from about 0.5 microns to about 50 microns, or more particularly,
microfibers may have an average diameter (from a sample of at least
10) of from about 2 microns to about 40 microns. Another frequently
used expression of fiber diameter is denier, which is defined as
grams per 9000 meters of a fiber. For example, the diameter of a
polypropylene fiber given in microns may be converted to denier by
squaring, and multiplying the result by 0.00629, thus, a 15 micron
polypropylene fiber has a denier of about 1.42 (15.sup.2
.times.0.00629=1.415).
As used herein the term "spunbonded fibers" refers to small
diameter fibers which are formed by extruding molten thermoplastic
material as filaments from a plurality of fine, usually circular
capillaries of a spinneret with the diameter of the extruded
filaments then being rapidly reduced as by, for example, in U.S.
Pat. No. 4,340,563 to Appel et al., and U.S. Pat. No. 3,692,618 to
Dorschner et al., U.S. Pat. No. 3,802,817 to Matsuki et al., U.S.
Pat. Nos. 3,338,992 and 3,341,394 to Kinney, U.S. Pat. No.
3,502,763 to Hartman, and U.S. Pat. No. 3,542,615 to Dobo et al.
Spunbond fibers are generally not tacky when they are deposited
onto a collecting surface. Spunbond fibers are generally continuous
and have average diameters (from a sample of at least 10) larger
than 7 microns, more particularly, between about 10 and 20
microns.
As used herein the term "meltblown fibers" means fibers formed by
extruding a molten thermoplastic material through a plurality of
fine, usually circular, die capillaries as molten threads or
filaments into converging high velocity gas (e.g. air) streams
which attenuate the filaments of molten thermoplastic material to
reduce their diameter, which may be to microfiber diameter.
Thereafter, the meltblown fibers are carried by the high velocity
gas stream and are deposited on a collecting surface to form a web
of randomly disbursed meltblown fibers. Such a process is
disclosed, for example, in U.S. Pat. No. 3,849,241. Meltblown
fibers are microfibers which may be continuous or discontinuous,
are generally smaller than 10 microns in average diameter, and are
generally tacky when deposited onto a collecting surface.
As used herein the term "polymer" generally includes but is not
limited to, homopolymers, copolymers, such as for example, block,
graft, random and alternating copolymers, terpolymers, etc. and
blends and modifications thereof. Furthermore, unless otherwise
specifically limited, the term "polymer" shall include all possible
geometrical configurations of the material. These configurations
include, but are not limited to isotactic, syndiotactic and random
symmetries.
As used herein, the term "machine direction" or MD means the length
of a fabric in the direction in which it is produced. The term
"cross machine direction" or CD means the width of fabric, i.e. a
direction generally perpendicular to the MD.
As used herein the term "monocomponent" fiber refers to a fiber
formed from one or more extruders using only one polymer. This is
not meant to exclude fibers formed from one polymer to which small
amounts of additives have been added for coloration, anti-static
properties, lubrication, hydrophilicity, etc. These additives, e.g.
titanium dioxide for coloration, are generally present in an amount
less than 5 weight percent and more typically about 2 weight
percent.
As used herein the term "conjugate fibers" refers to fibers which
have been formed from at least two polymers extruded from separate
extruders but spun together to form one fiber. Conjugate fibers are
also sometimes referred to as multicomponent or bicomponent fibers.
The polymers are usually different from each other though conjugate
fibers may be monocomponent fibers. The polymers are arranged in
substantially constantly positioned distinct zones across the
cross-section of the conjugate fibers and extend continuously along
the length of the conjugate fibers. The configuration of such a
conjugate fiber may be, for example, a sheath/core arrangement
wherein one polymer is surrounded by another or may be a side by
side arrangement or an "islands-in-the-sea" arrangement. Conjugate
fibers are taught in U.S. Pat. No. 5,108,820 to Kaneko et al., U.S.
Pat. No. 5,336,552 to Strack et al., and U.S. Pat. No. 5,382,400 to
Pike et al. For two component fibers, the polymers may be present
in ratios of 75/25, 50/50, 25/75 or any other desired ratios.
As used herein the term "biconstituent fibers" refers to fibers
which have been formed from at least two polymers extruded from the
same extruder as a blend. The term "blend" is defined below.
Biconstituent fibers do not have the various polymer components
arranged in relatively constantly positioned distinct zones across
the cross-sectional area of the fiber and the various polymers are
usually not continuous along the entire length of the fiber,
instead usually forming fibrils or protofibrils which start and end
at random. Biconstituent fibers are sometimes also referred to as
multiconstituent fibers. Fibers of this general type are discussed
in, for example, U.S. Pat. No. 5,108,827 to Gessner. Conjugate and
biconstituent fibers are also discussed in the textbook Polymer
Blends and Composites by John A. Manson and Leslie H. Sperling,
copyright 1976 by Plenum Press, a division of Plenum Publishing
Corporation of New York, IBSN 0-306-30831-2, at pages 273 through
277.
As used herein the term "blend" means a mixture of two or more
polymers while the term "alloy" means a sub-class of blends wherein
the components are immiscible but have been compatibilized.
"Miscibility" and "immiscibility" are defined as blends having
negative and positive values, respectively, for the free energy of
mixing. Further, "compatibilization" is defined as the process of
modifying the interfacial properties of an immiscible polymer blend
in order to make an alloy.
As used herein, the term "compaction roll" means a set or rollers
above and below the web to compact the web as a way of pre- or
primarily bonding a just produced spunbond web in order to give it
sufficient integrity for further processing, but not the relatively
strong bonding of secondary bonding processes like TAB, thermal
bonding, hydroentanglement and ultrasonic bonding. Compaction rolls
slightly squeeze the web in order to increase its self-adherence
and thereby its integrity. Compaction rolls perform this function
well but have a number of drawbacks. One such drawback is that
compaction rolls do indeed compact the web, causing a decrease in
bulk or loft in the fabric which may be undesirable for the use
desired. A second and more serious drawback to compaction rolls is
that the fabric will sometimes wrap around one or both of the
rolls, causing a shutdown of the fabric production line for
cleaning of the rolls, with the accompanying obvious loss in
production during the down time. A third drawback to compaction
rolls is that if a slight imperfection is produced in formation of
the web, such as a drop of polymer being formed into the web, the
compaction roll can force the drop into the foraminous belt, onto
which most webs are formed, causing an imperfection in the belt and
ruining it.
As used herein, the term "hot air knife" or HAK means a process of
pre- or primarily treating a just produced spunbond web in order to
give it sufficient integrity for further processing but not the
relatively strong bonding of secondary bonding processes like TAB,
thermal bonding, hydroentanglement and ultrasonic bonding. A hot
air knife is a device which focuses a stream of heated air at a
very high flow rate, generally from about 1000 to about 10000 feet
per minute (fpm) (305 to 3050 meters per minute), directed at the
nonwoven web immediately after its formation. The air temperature
is generally between about 200.degree. and 550.degree. F.
(93.degree. and 290.degree. C.) for the thermoplastic polymers
commonly used in spunbonding. The HAK's focused stream of air is
arranged and directed by at least one slot of about 1/8 to 1 inches
(3 to 25 mm) in width, particularly about 3/8 inch (9.4 mm),
serving as the exit for the heated air towards the web, with the
slot running in a substantially cross-machine direction over
substantially the entire width of the web. In other embodiments,
there may be a plurality of slots arranged next to each other or
separated by a slight gap. The at least one slot is preferably,
though not essentially, continuous, and may be comprised of, for
example, closely spaced holes. The HAK has a plenum to distribute
and contain the heated air prior to its exiting the slot. The
plenum pressure of the HAK is preferably between about 1.0 and 12.0
inches of water (2 to 22 mmHg), and the HAK is positioned between
about 0.25 and 10 inches and more preferably 0.75 to 3.0 inches (19
to 76 mm) above the forming wire. In a particular embodiment the
HAK plenum's cross sectional area for cross-directional flow (i.e.
the plenum cross sectional area in the machine direction) is at
least twice the total slot exit area. Since the foraminous wire
onto which spunbond polymer is formed generally moves at a high
rate of speed, the time of exposure of any particular part of the
web to the air discharged from the hot air knife is less a tenth of
a second and generally about a hundredth of a second in contrast
with the through air bonding process which has a much larger dwell
time. The HAK process has a great range of variability and
controllability of at least the air temperature, air velocity and
distance from the HAK plenum to the web.
As used herein, through air bonding or "TAB" means a process of
bonding a nonwoven conjugate fiber web in which air which is
sufficiently hot to melt one of the polymers of which the fibers of
the web are made is forced through the web. The air velocity is
between 100 and 500 feet per minute and the dwell time may be as
long as 6 seconds. The melting and resolidification of the polymer
provides the bonding. Through air bonding is generally regarded a
second step bonding process. Since TAB requires the melting of at
least one component to accomplish bonding, it is restricted to webs
with at least two components like conjugate fibers or those which
include an adhesive.
As used herein, the term "stitchbonded" means, for example, the
stitching of a material in accordance with U.S. Pat. No. 4,891,957
to Strack et al. or U.S. Pat. No. 4,631,933 to Carey, Jr.
As used herein, "ultrasonic bonding" means a process performed, for
example, by passing the fabric between a sonic horn and anvil roll
as illustrated in U.S. Pat. No. 4,374,888 to Bornslaeger.
As used herein "thermal point bonding" involves passing a fabric or
web of fibers to be bonded between a heated calender roll and an
anvil roll. The calender roll is usually, though not always,
patterned in some way so that the entire fabric is not bonded
across its entire surface, and the anvil roll is usually flat. As a
result, various patterns for calender rolls have been developed for
functional as well as aesthetic reasons. One example of a pattern
has points and is the Hansen Pennings or "H&P" pattern with
about a 30% bond area with about 200 bonds/square inch as taught in
U.S. Pat. No. 3,855,046 to Hansen and Pennings. The H&P pattern
has square point or pin bonding areas wherein each pin has a side
dimension of 0.038 inches (0.965 mm), a spacing of 0.070 inches
(1.778 mm) between pins, and a depth of bonding of 0.023 inches
(0.584 mm). The resulting pattern has a bonded area of about 29.5%.
Another typical point bonding pattern is the expanded Hansen
Pennings or "EHP" bond pattern which produces a 15% bond area with
a square pin having a side dimension of 0.037 inches (0.94 mm), a
pin spacing of 0.097 inches (2.464 mm) and a depth of 0.039 inches
(0.991 mm). Another typical point bonding pattern designated "714"
has square pin bonding areas wherein each pin has a side dimension
of 0.023 inches, a spacing of 0.062 inches (1.575 mm) between pins,
and a depth of bonding of 0.033 inches (0.838 mm). The resulting
pattern has a bonded area of about 15%. Yet another common pattern
is the C-Star pattern which has a bond area of about 16.9%. The
C-Star pattern has a cross-directional bar or "corduroy" design
interrupted by shooting stars. Other common patterns include a
diamond pattern with repeating and slightly offset diamonds with
about a 16% bond area and a wire weave pattern looking as the name
suggests, e.g. like a window screen, with about a 19% bond area.
Typically, the percent bonding area varies from around 10% to
around 30% of the area of the fabric laminate web. As in well known
in the art, the spot bonding holds the laminate layers together as
well as imparts integrity to each individual layer by bonding
filaments and/or fibers within each layer.
As used herein, the term "bonding window" means the range of
temperature of the calender rolls used to bond the nonwoven fabric
together, over which such bonding is successful. For polypropylene
spunbond, this bonding window is typically from about 270.degree.
F. to about 310.degree. F. (132.degree. C. to 154.degree. C.).
Below about 270.degree. F. the polypropylene is not hot enough to
melt and bond and above about 310.degree. F. the polypropylene will
melt excessively and can stick to the calender rolls. Polyethylene
has an even narrower bonding window.
As used herein the term "recover" refers to a contraction of a
stretched material upon termination of a biasing force following
stretching of the material by application of the biasing force. For
example, if a material having a relaxed, unbiased length of one (1)
inch was elongated 50 percent by stretching to a length of one and
one half (1.5) inches the material would have a stretched length
that is 150 percent of its relaxed length. If this exemplary
stretched material contracted, that is recovered to a length of one
and one tenth (1.1) inches after release of the biasing and
stretching force, the material would have recovered 80 percent (0.4
inch) of its elongation.
As used herein, the terms "necking" or "neck stretching"
interchangeably refer to a method of elongating a nonwoven fabric,
generally in the machine direction, to reduce its width in a
controlled manner to a desired amount. The controlled stretching
may take place under cool, room temperature or greater temperatures
and is limited to an increase in overall dimension in the direction
being stretched up to the elongation required to break the fabric,
which in most cases is about 1.2 to 1.4 times. When relaxed, the
web retracts toward its original dimensions. Such a process is
disclosed, for example, in U.S. Pat. No. 4,443,513 to Meitner and
Notheis, and U.S. Pat. No. 4,965,122, 4,981,747 and 5,114,781 to
Morman.
As used herein, the terms "elastic" and "elastomeric" when
referring to a fiber, film or fabric mean a material which upon
application of a biasing force, is stretchable to a stretched,
biased length which is at least about 150 percent, or one and a
half times, its relaxed, unstretched length, and which will recover
at least 50 percent of its elongation upon release of the
stretching, biasing force.
As used herein the term "composite elastic material" refers to an
elastic material which may be a multicomponent material or a
multilayer material. For example, a multilayer material may have at
least one elastic layer joined to at least one gatherable layer at
least at two locations so that the gatherable layer is gathered
between the locations where it is joined to the elastic layer. Such
a multilayer composite elastic material may be stretched to the
extent that the nonelastic material gathered between the bond
locations allows the elastic material to elongate. One type of
multilayer composite elastic material is disclosed, for example, by
U.S. Pat. No. 4,720,415 to Vander Wielen et al., which is hereby
incorporated by reference in its entirety, and in which multiple
layers of the same polymer produced from multiple banks of
extruders are used. Other composite elastic materials are disclosed
in U.S. Pat. No. 4,789,699 to Kieffer et al., U.S. Pat. No.
4,781,966 to Taylor and U.S. Pat. Nos. 4,657,802 and 4,652,487 to
Morman and 4,655,760 and 4,692,371 to Morman et al. A composite
elastic material may also be one in which the gatherable web is a
neckable material which is necked, and then is joined to an elastic
sheet such as described in U.S. Pat. Nos. 5,226,992, 4,981,747,
4,965,122 and 5,336,545 to Morman.
As used herein, the term "garment" means any type of non-medically
oriented apparel which may be worn. This includes industrial work
wear and coveralls, undergarments, pants, shirts, jackets, gloves,
socks, and the like.
As used herein, the term "infection control product" means
medically oriented items such as surgical gowns and drapes, face
masks, head coverings like bouffant caps, surgical caps and hoods,
footwear like shoe coverings, boot covers and slippers, wound
dressings, bandages, sterilization wraps, wipers, garments like lab
coats, coveralls, aprons and jackets, patient bedding, stretcher
and bassinet sheets, and the like.
As used herein, the term "personal care product" means diapers,
training pants, absorbent underpants, adult incontinence products,
and feminine hygiene products.
As used herein, the term "protective cover" means a cover for
vehicles such as cars, trucks, boats, airplanes, motorcycles,
bicycles, golf carts, etc., covers for equipment often left
outdoors like grills, yard and garden equipment (mowers,
roto-tillers, etc.) and lawn furniture, as well as floor coverings,
table cloths and picnic area covers.
TEST METHODS
Melt Flow Rate: The melt flow rate (MFR) is a measure of the
viscosity of a polymer. The MFR is expressed as the weight of
material which flows from a capillary of known dimensions under a
specified load or shear rate for a measured period of time and is
measured in grams/10 minutes at a set temperature and load
according to, for example, ASTM test 1238-90b.
Cyclic testing: Cyclic testing is performed using a Sintech 2
computerized material testing system available from Sintech
Incorporated of Stoughton, Mass.
In the elongation or stretch to stop test, a 3 inch by 6 inch (76
mm by 152 mm) sample, with the larger dimension being the machine
direction, is placed in the jaws of the Sintech 2 machine using a
gap of 50 mm between the jaws. The sample is then pulled to a stop
load of 2000 gms with a crosshead speed of about 500 mm per minute.
The elongation in percent relative to the unstretched length at
2000 gms is the stretch to stop value.
The elongation at stop test also yields the value for elongation at
intercept. The elongation at intercept is the percent stretch at
the upper inflection point of the load versus percent stretch
graph. The value of 75 percent of the elongation at intercept is
used to determine the maximum percent the sample with then be
stretched in the cycling test.
In the cyclic testing, a material is taken to a fixed extension
corresponding to 75 percent of the elongation at intercept for 5
times, and allowed to return to its original dimensions if it will
do so. The measurements taken are the load at elongation,
hysteresis loss and load at return. This is used to develop a
graphical representation of the results, with load on the y axis
and elongation on the x axis, as for example in FIGS. 1, 2, and 3.
This graph yields a curve with an area thereunder called the Total
Energy Absorbed or "TEA". The ratio of the TEA curves for a sample
for various cycles is a value independent of material, basis weight
and sample width that can be compared to other samples.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 shows a TEA curve of a composite elastic laminate of the
Control. FIG. 2 shows a TEA curve of a composite elastic laminate
of Example 1. FIG. 3 shows a TEA curve of a composite elastic
laminate of Example 2. The Y-axis indicates units of load in grams.
The X-axis is the elongation in percent. FIG. 4 shows a schematic
diagram of an in-line manufacturing process suitable for the
production of a composite elastic material.
DETAILED DESCRIPTION
Thermoplastic polymers are useful in the production of films,
fibers and webs for use in a variety of products such as personal
care items, infection control products, garments and protective
covers. In many applications it is desirable that the film, fiber
or web be elastic so that the products made with the film, fiber or
web can conform to an object or so that it may stretch somewhat
without failing.
Elastomeric polymers have been used in the past for such
applications but are somewhat difficult to process. U.S. Pat. No.
4,663,220 to Wisneski et al. discloses a method of improving the
processibility of an elastomeric polymer through the addition of a
polyolefin, particularly polyethylene, processing aid. Further,
such products have a particular range of stretch and recovery
characteristics.
The Applicant has produced a laminate having at least one layer
made of a new class of polymers having different stretch and
recovery characteristics than those previously used. This laminates
has properties which are particularly useful and further, the
structure is such that it allows the user to tailor the properties
of the film, fiber or web laminate to her exact requirements.
The new class of polymers is referred to as "metallocene" polymers
or as produced according to the metallocene process. The
metallocene process generally uses a metallocene catalyst which is
activated, i.e. ionized, by a co-catalyst.
Metallocene catalysts include bis(n-butylcyclopentadienyl)titanium
dichloride, bis(n-butylcyclopentadienyl)zirconium dichloride,
bis(cyclopentadienyl)scandium chloride, bis(indenyl)zirconium
dichloride, bis(methylcyclopentadienyl)titanium dichloride,
bis(methylcyclopentadienyl)zirconium dichloride, cobaltocene,
cyclopentadienyltitanium trichloride, ferrocene, hafnocene
dichloride, isopropyl(cyclopentadienyl,-1-flourenyl)zirconium
dichloride, molybdocene dichloride, nickelocene, niobocene
dichloride, ruthenocene, titanocene dichloride, zirconocene
chloride hydride, zirconocene dichloride, among others. A more
exhaustive list of such compounds is included in U.S. Pat. No.
5,374,696 to Rosen et al. and assigned to the Dow Chemical Company.
Such compounds are also discussed in U.S. Pat. No. 5,064,802 to
Stevens et al. and also assigned to Dow.
The metallocene process, and particularly the catalysts and
catalyst support systems are the subject of a number of patents.
U.S. Pat. No. 4,542,199 to Kaminsky et al. describes a procedure
wherein a co-catalyst like methylaluminoxane (MAO) is added to
toluene, the metallocene catalyst of the general formula
(cyclopentadienyl)2MeRHal wherein Me is a transition metal, Hal is
a halogen and R is cyclopentadienyl or a C1 to C6 alkyl radical or
a halogen, is added, and ethylene is then added to form
polyethylene. U.S. Pat. No. 5,189,192 to LaPointe et al. and
assigned to Dow Chemical describes a process for preparing addition
polymerization catalysts via metal center oxidation. U.S. Pat. No.
5,352,749 to Exxon Chemical Patents, Inc. describes a method for
polymerizing monomers in fluidized beds. U.S. Pat. No. 5,349,100
describes chiral metallocene compounds and preparation thereof by
creation of a chiral center by enantioselective hydride
transfer.
Co-catalysts are materials such as methylaluminoxane (MAO) which is
the most common, other alkylaluminums and boron containing
compounds like tris(pentafluorophenyl)boron, lithium
tetrakis(pentafluorophenyl)boron, and dimethylanilinium
tetrakis(pentafluorophenyl)boron. Research is continuing on other
co-catalyst systems or the possibility of minimizing or even
eliminating the alkylaluminums because of handling and product
contamination issues. The important point is that the metallocene
catalyst be activated or ionized to a cationic form for reaction
with the monomer(s) to be polymerized.
Polymers produced using metallocene catalysts have the unique
advantage of having a very narrow molecular weight range. FIG. 1
shows a typical molecular weight distribution for a Ziegler-Natta
catalyst versus a metallocene type catalyst with the metallocene
catalyst yielding the narrower curve. Polydispersity numbers
(Mw/Mn) of below 4 and even below 2 are possible for metallocene
produced polymers. These polymers also have a narrow short chain
branching distribution when compared to otherwise similar
Ziegler-Natta produced type polymers.
It is also possible using a metallocene catalyst system to control
the isotacticity of the polymer quite closely when stereo selective
metallocene catalysts are employed. In fact, polymers have been
produced having an isotacticity of in excess of 99 percent. It is
also possible to produce highly syndiotactic polypropylene using
this system.
Controlling the isotacticity of a polymer can also result in the
production of a polymer which contains blocks of isotactic and
blocks of atactic material alternating over the length of the
polymer chain. This construction results in an elastic polymer by
virtue of the atactic portion. Such polymer synthesis is discussed
in the journal Science, vol. 267, (13 Jan., 1995) at p. 191 in an
article by K. B. Wagner. Wagner, in discussing the work of Coates
and Waymouth, explains that the catalyst oscillates between the
stereochemical forms resulting in a polymer chain having running
lengths of isotactic sterocenters connected to running lengths of
atactic centers. Isotactic dominance is reduced producing
elasticity. Geoffrey W. Coates and Robert M. Waymouth, in an
article entitled "Oscillating Stereocontrol: A Strategy for the
Synthesis of Thermoplastic Elastomeric Polypropylene" at page 217
in the same issue, discuss their work in which they used
metallocene bis(2-phenylindenyl)-zirconium dichloride in the
presence of methylaluminoxane (MAO), and, by varying the pressure
and temperature in the reactor, oscillate the polymer form between
isotactic and atactic.
Commercial production of metallocene polymers is somewhat limited
but growing. Such polymers are available from Exxon Chemical
Company of Baytown, Tex. under the trade names EXXPOL.RTM. and
ACHIEVE.TM. for polypropylene based polymers and EXACT.RTM. and
EXCEED.TM. for polyethylene based polymers. Dow Chemical Company of
Midland, Mich. has polymers commercially available under the name
ENGAGE.RTM.. These materials are believed to be produced using
non-stereo selective metallocene catalysts. Exxon generally refers
to their metallocene catalyst technology as "single site" catalysts
while Dow refers to theirs as "constrained geometry" catalysts
under the name INSITE.RTM. to distinguish them from traditional
Ziegler-Natta catalysts which have multiple reaction sites. Other
manufacturers such as Fina Oil, BASF, Amoco, Hoechst and Mobil are
active in this area and it is believed that the availability of
polymers produced according to this technology will grow
substantially in the next decade. In the practice of the instant
invention, elastic polyolefins like polypropylene and polyethylene
are suitable.
Regarding metallocene based elastomeric polymers, U.S. Pat. No.
5,204,429 to Kaminsky et al. describes a process which may produce
elastic copolymers from cycloolefins and linear olefins using a
catalyst which is a sterorigid chiral metallocene transition metal
compound and an aluminoxane. The polymerization is carried out in
an inert solvent such as an aliphatic or cycloaliphatic hydrocarbon
such as toluene. The reaction may also occur in the gas phase using
the monomers to be polymerized as the solvent. U.S. Pat. Nos.
5,278,272 and 5,272,236, both to Lai et al., assigned to Dow
Chemical and entitled "Elastic Substantially Linear Olefin
Polymers" describe polymers having particular elastic properties.
Dow also commercially produces a line of elastomeric polyolefins
under the trade name ENGAGE.RTM..
Other elastomeric thermoplastic polymers useful in the practice of
this invention may be those made from block copolymers such as
polyurethanes, copolyetheresters, polyamide polyether block
copolymers, ethylene vinyl acetates (EVA), block copolymers having
the general formula A-B-A', A-B-A-B, or A-B like
copoly(styrene/ethylene-butylene),
(polystyrene/poly(ethylene-butylene)/polystyrene),
poly(styrene/ethylene-butylene/styrene) and the like.
Useful elastomeric resins include block copolymers having the
general formula A-B-A', or A-B, where A and A' are each a
thermoplastic polymer endblock which contains a styrenic moiety
such as a poly (vinyl arene) and where B is an elastomeric polymer
midblock such as a conjugated diene or a lower alkene polymer.
Block copolymers of the A-B-A' type can have different or the same
thermoplastic block polymers for the A and A' blocks, and the
present block copolymers are intended to embrace linear, branched
and radial block copolymers. In this regard, the radial block
copolymers may be designated (A-B).sub.m -X, wherein X is a
polyfunctional atom or molecule and in which each (A-B).sub.m -
radiates from X in a way that A is an endblock. In the radial block
copolymer, X may be an organic or inorganic polyfunctional atom or
molecule and m is an integer having the same value as the
functional group originally present in X. It is usually at least 3,
and is frequently 4 or 5, but not limited thereto. Thus, in the
present invention, the expression "block copolymer", and
particularly "A-B-A'" and "A-B" block copolymer, is intended to
embrace all block copolymers having such rubbery blocks and
thermoplastic blocks as discussed above, which can be extruded
(e.g., by meltblowing), and without limitation as to the number of
blocks. The elastomeric nonwoven web may be formed from, for
example, elastomeric
(polystyrene/poly(ethylene-butylene)/polystyrene) block copolymers.
Commercial examples of such elastomeric copolymers are, for
example, those known as KRATON.RTM. materials which are available
from Shell Chemical Company of Houston, Tex. KRATON.RTM. block
copolymers are available in several different formulations, a
number of which are identified in U.S. Pat. No. 4,663,220, hereby
incorporated by reference.
Polymers composed of an elastomeric A-B-A'-B' tetrablock copolymer
may also be used in the practice of this invention. Such polymers
are discussed in U.S. Pat. No. 5,332,613 to Taylor et al. In such
polymers, A is a thermoplastic polymer block and B is an isoprene
monomer unit hydrogenated to substantially a
poly(ethylene-propylene) monomer unit. An example of such a
tetrablock copolymer is a
styrene-poly(ethylene-propylene)-styrene-poly(ethylene-propylene)
or SEPSEP elastomeric block copolymer available from the Shell
Chemical Company of Houston, Tex. under the trade designation
KRATON.RTM. G-1657.
The thermoplastic copolyester elastomers include copolyetheresters
having the general formula: ##STR1## where "G" is selected from the
group consisting of poly(oxyethylene)-alpha,omega-diol,
poly(oxypropylene)-alpha,omega-diol,
poly(oxytetramethylene)-alpha,omega-diol and "a", "m" and "n" are
positive integers. Such materials generally have an elongation at
break of from about 600 percent to 750 percent when measured in
accordance with ASTM D-638 and a melt point of from about
350.degree. F. to about 400.degree. F. (176.degree. to 205.degree.
C.) when measured in accordance with ASTM D-2117.
Commercial examples of such copolyester materials are, for example,
those known as ARNITEL.RTM., formerly available from Akzo Plastics
of Arnhem, Holland and now available from DSM of Sittard, Holland,
or those known as HYTREL.RTM. which are available from E.I. DuPont
de Nemours of Wilmington, Del. Formation of an elastomeric nonwoven
web from polyester elastomeric materials is disclosed in, for
example, U.S. Pat. No. 4,741,949 to Morman et al., hereby
incorporated by reference.
Other exemplary elastomeric materials which may be used include
polyurethane elastomeric materials such as, for example, those
available under the trademark ESTANE.RTM. from B.F. Goodrich &
Co. or MORTHANE.RTM. from Morton Thiokol Corp., polyamide polyether
block copolymer such as, for example, that known as PEBAX.RTM.,
available from Atochem Inc. Polymers Division (RILSAN.RTM.), of
Glen Rock, N.J. and polyester elastomeric materials such as, for
example, those available under the trade designation HYTREL.RTM.
from E.I. DuPont De Nemours & Company.
Elastomeric polymers also include copolymers of ethylene and at
least one vinyl monomer such as, for example, vinyl acetates,
unsaturated aliphatic monocarboxylic acids, and esters of such
monocarboxylic acids. The elastomeric copolymers and formation of
elastomeric nonwoven webs from those elastomeric copolymers are
disclosed in, for example, U.S. Pat. No. 4,803,117.
It is also possible to have other materials blended with the
elastomer used to produce a layer according to this invention like
fluorocarbon chemicals to enhance chemical repellence which may be,
for example, any of those taught in U.S. Pat. No. 5,178,931, fire
retardants for increased resistance to fire and/or pigments to give
each layer the same or distinct colors. Fire retardants and
pigments for spunbond and meltblown thermoplastic polymers are
known in the art and are internal additives. A pigment, if used, is
generally present in an amount less than 5 weight percent of the
layer while other materials may be present in a cumulative amount
less than 25 weight percent.
Items made from the laminates of this invention may also have
topical treatments applied to it for more specialized functions.
Such topical treatments and their methods of application are known
in the art and include, for example, alcohol repellence treatments,
anti-static treatments and the like, applied by spraying, dipping,
etc. An example of such a topical treatment is the application of
Zelec.RTM. antistat (available from E.I. DuPont, Wilmington,
Del.).
When the laminates of this invention are in the form of nonwoven
fabric, they may be produced by the meltblowing or spunbonding
processes which are well known in the art. These processes
generally use an extruder to supply melted thermoplastic polymer to
a spinneret where the polymer is fiberized to yield fibers which
may be staple length or longer. The fibers are then drawn, usually
pneumatically, and deposited on a moving foraminous mat or belt to
form the nonwoven fabric. The fibers produced in the spunbond and
meltblown processes are microfibers as defined above.
Spunbond nonwoven fabrics are generally pre- or primarily bonded in
some manner as they are produced in order to give them sufficient
structural integrity to withstand the rigors of further processing
into a finished product. This primary bonding may be done by
compaction rollers or by hot-air knife. Secondary bonding can be
accomplished in a number of ways such as hydroentanglement,
needling, ultrasonic bonding, adhesive bonding, stitchbonding,
through-air bonding and thermal bonding.
Multiple layers of meltblown fabrics may be bonded by
needlepunching, ultrasonic bonding, adhesive attachment, thermal
bondiing and extrusion coating.
An example of a multilayer laminate is an embodiment wherein some
of the layers are spunbond and some meltblown such as a
spunbond/meltblown/spunbond (SMS) laminate as disclosed in U.S.
Pat. No. 4,041,203 to Brock et al., U.S. Pat. No. 5,169,706 to
Collier, et al, and U.S. Pat. No. 4,374,888 to Bornslaeger which
are hereby incorporated by reference in their entirety. Such a
laminate may be made by sequentially depositing onto a moving
forming belt first a spunbond fabric layer, then a meltblown fabric
layer and last another spunbond layer and then bonding the laminate
in a manner described above. Alternatively, the fabric layers may
be made individually, collected in rolls, and combined in a
separate bonding step such as that disclosed in U.S. Pat. No.
4,720,415, hereby incorporated by reference in its entirety. Such
multilayer laminates usually have a basis weight of from about 0.1
to 12 osy (6 to 400 gsm), or more particularly from about 0.75 to
about 3 osy.
The composite elastic material of this invention has at least one
layer of an elastic polyolefin with at least one layer of another
type of elastic polymer and a gatherable web which is joined to the
elastic webs. This may be done while the elastic webs are stretched
and or while the gatherable web is necked. The elastic polyolefin
is preferably made by the metallocene process. There may be two
gatherable webs; one on each side of the elastic layers, and there
may be multiple elastic layers. The elastic layers may be arranged,
for example, with the elastic polyolefin material in the center, an
elastic layer of another type of polymer on either side of the
elastic polyolefin material, and finally a gatherable layer bonded
to each of the other elastic layers. The laminate may have the
elastic polyolefin layer in the center, other elastic layers on
either side and then additional layers of elastic polyolefin on
either side of the other elastic layers and finally the gatherable
layers as outer layers. The number and arrangement of the layers is
limited only by equipment and imagination.
The gatherable web of this invention may be a spunbond web of, for
example, a polyolefin like polypropylene, or may be any other
suitable material which lacks the characteristics of an elastic as
defined above.
FIG. 4 shows a schematic diagram of a continuous manufacturing
in-line process for stretch bonding elastic and gatherable webs
into a laminate wherein there are two gatherable webs on each
opposite side of a stretchable web of two elastomeric polymers. In
the Figure, an elastic polymer is deposited onto a forming wire 2
from each of two meltblowing spinnerets 1 producing an elastic web
3. The forming wire 2 moves at a certain first speed as the layers
are deposited. The elastic web 3 moves forward to pass through
bonder rolls 6, 7 where the elastic web 3 is combined with, in this
case, two, gatherable webs 4, 5 unwould from supply rolls. The
bonder rolls 6, 7 are shown as being comprised of a patterned
calender roll 6 and a smooth anvil roll 7 but other methods and
arrangements as noted herein may be used. The webs 3, 4, 5 travel
in the direction indicated by the arrows associated with the rolls
for forming wire 2 and the supply rolls, respectively. The elastic
web 3 is stretched to the desired amount by having the bonder rolls
6, 7 rotate at a speed greater than that at which the forming wire
2 moves, producing a bonder/wire ratio of speed. The pressure
between the rollers 6, 7 bonds the gatherable webs 4, 5 to the
elastic web 3 to form a composite elastic material 8. The composite
elastic material 8 is then wound up on a winder 9.
The inventors have found that a laminate wherein at least one layer
is made of an elastomeric polyolefin preferably having a
polydispersity of less than 4, with at least one other elastomeric
polymer layer and a non-elastic gatherable web, allows the precise
control of the elastomeric properties, e.g. hysteresis, of a
product produced from such a laminate. In particular a laminate
having one layer of an elastomeric polyolefin with one layer of
elastomeric poly(styrene/ethylene-butylene/styrene) block copolymer
and a polypropylene gatherable web on either side produces a
particularly good blend of stretch and recovery
characteristics.
In order to illustrate the advantages of laminates according to
this invention, the following Examples and Controls were developed.
Note that the process conditions used to produce these laminates
are given in Table 1.
CONTROL
Two samples of a composite elastic material were produced using 0.4
osy (13.6 gsm) polypropylene spunbond outer layers as the
gatherable webs and an elastic meltblown inner layer of Shell's
Kraton.RTM. G-2755 poly(styrene/ethylene-butylene/styrene) or SEBS
resin. The layers were thermally bonded to produce the laminate
with a 13 percent bond area pattern while the elastic meltblown
layer was stretched using the bonder/wire ratio as shown in the
Table.
EXAMPLE 1
Three samples of a composite elastic material were produced using
0.4 osy (13.6 gsm) polypropylene spunbond outer layers as the
gatherable webs and a meltblown inner layer of Dow's ENGAGE.RTM.
58200.02 metallocene polymer having a melt flow index of 30
grams/10 minutes at 190.degree. C. and and 2160 gm load. The layers
were thermally bonded to produce the laminate with a 13 percent
bond area pattern while the elastic meltblown layer was stretched
using the bonder/wire ratio as shown in the Table.
EXAMPLE 2
Two samples of a composite elastic material were produced using 0.4
osy (13.6 gsm) polypropylene spunbond outer layers as the
gatherable webs and a meltblown inner layer of Shell's Kraton.RTM.
G-2755 polymer and a second meltblown inner layer of Dow's
ENGAGE.RTM. 58200.02 polymer. The layers were thermally bonded to
produce the laminate with a 13 percent bond area pattern while the
elastic meltblown layer was stretched using the bonder/wire ratio
as shown in the Table.
The Control and Examples were tested for stretch properties
according to the cyclic testing method described above under "Test
Methods" and the results are given in Table 1. In the Table, the
abbreviation EXT means "extension", RET means "return", STS means
"stretch to stop", MB means "meltblown" and BW means "basis
weight".
TABLE 1
__________________________________________________________________________
Basis Cycle Load Load Weight Cycle Cycle 5/1 at Cycling at Load at
Load at Bonder Bonding in Lam- Stretch Cycle 1 1 5 EXT/ Inter-
Elonga- 30% 40% cycling Melt Air to Temp. inate to Stop EXT RET EXT
TEA cept tion Elong. Elong. Elonga- Temp. Temp. wire F. GSM % TEA
TEA TEA Ratio g % g g tion g F. F. ratio (set)
__________________________________________________________________________
Ex- 64 86.9 30.5 20.4 21.7 0.7115 854 60 420 515 680 455 491 2.9
135 ample 2 Ex- 56 111.3 44.5 28.1 30.8 0.6921 927 80 368 461 735
455 491 3.8 135 ample 2 Ex- 65 83.3 30.9 20.2 20.3 0.6570 871 60
415 527 730 466 477 4.2 145 ample 1 Ex- 70 74.2 27.2 16.4 16.7
0.6139 813 60 356 462 681 431 438 2.8 170 ample 1 Ex- 65 90 28.9
17.6 17.9 0.6194 774 60 378 497 725 401 438 4.2 170 ample 1 Control
47 151.4 30.7 20 21.2 0.6906 957 60 436 513 618 -500 474 3.2 130
Control 47 151.4 49.9 29.3 31.8 0.6373 957 80 460 535 716 -500 474
4.5 130
__________________________________________________________________________
The Table shows that by providing layers of elastomeric polyolefin
and non-polyolefin elastomer in a laminate, good control of the
stretch and recovery properties is possible and it is possible to
produce a laminate with more or less stretch and better or worse
recovery than other laminates. This control allows the users of
products made from the laminates of this invention to more exactly
tailor their products to the needs of their customers, thus also
producing for cost savings since the product will provide the
required stretch, but not more or less than required. For example,
producing a laminate having an elastic polyolefin layer with a
layer of elastomeric polyurethane on each side will produce a
laminate with different stretch and recovery characteristics than a
laminate with an elastic polyolefin layer with a layer of
elastomeric SEBS on each side. Placing an elastic polyolefin layer
on either side of an elastic polyetherester will provide a laminate
with different hysteresis from the previous two.
Although only a few exemplary embodiments of this invention have
been described in detail above, those skilled in the art will
readily appreciate that many modifications are possible in the
exemplary embodiments without materially departing from the novel
teachings and advantages of this invention. Accordingly, all such
modifications are intended to be included within the scope of this
invention as defined in the following claims. In the claims, means
plus function claims are intended to cover the structures described
herein as performing the recited function and not only structural
equivalents but also equivalent structures. Thus although a nail
and a screw may not be structural equivalents in that a nail
employs a cylindrical surface to secure wooden parts together,
whereas a screw employs a helical surface, in the environment of
fastening wooden parts, a nail and a screw may be equivalent
structures.
* * * * *